A fundamental problem of known filling systems is that of preventing ambient air from penetrating through a dispensing opening and into the liquid channel of valve chamber of a filling element. It is important to do so because air that has penetrated into the liquid channel causes air bubbles that eventually rise into the product lines and finally into the boiler that supplies liquid charge to all the filling elements of the filling system. This can lead to contamination of charge in the product lines and in the boiler. It can also lead to loss of measurement accuracy because rising air bubbles may interfere with operation of flow meters or other measurement devices.
In known filling elements, an actuator opens the liquid valve as quickly and completely as possible. In these known filling elements, a valve can be completely open within as few as 50 milliseconds.
A liquid valve has a gap across its opening. The width of this gap when the valve is fully open is known to have an effect on how much air penetrates into the channel. According to generally established opinion, an effective way to prevent air from penetrating into the liquid channel of the filling element is to make make the width of this gap as small as possible. In most known filling systems, the gap width is approximately 1.0 mm to 1.5 mm.
An additional way to suppress entry of ambient air is to use a gas lock in the liquid channel. A gas lock has a multiplicity of passages, each with minimum flow cross section. These narrow passages make it difficult for ambient air to penetrate and thus suppress formation of air bubbles rising in the filling element and in the product lines.
These known free-jet filling elements are effective when the contents of the container are purely liquid. However, in some cases, the contents include solid constituents. For example, fruit juices may include suspended solids such as fruit flesh and/or fruit fibers, or pulp. These products require gap sizes or gap widths for the gap of the open filling element of more than 3 millimeters. This is much greater than the usual range of 1-1.5 millimeters that has been found effective to reduce ingress of air.
Obviously, making the gap wide enough to accommodate fruit pulp and the like would likely lead to the penetration of air bubbles into the liquid channel and via the product channels or lines into the product boiler.